Add folder and search pattern support to AzureSignTool

[MarcWeintraub]

This commit introduces two new properties, Folder and SearchPatterns, to the AzureSignTool namespace in Program.cs, enabling users to specify a folder and search patterns for file processing. A new method, GetFolderSerachPattern, retrieves files based on these patterns, while a static method, AddArray, facilitates adding multiple items to a HashSet. The AllFiles property is updated to utilize this new method, and command-line argument parsing is modified to include the new options. Additionally, validation checks ensure the specified folder exists and that search patterns are provided when a folder is specified.